What is the pink slime in my shower or toilet?

The film is Serratia marcescens, a bacterium that lives in soil, dust, and air almost everywhere. Its pink, orange, or reddish color comes from a natural pigment the bacteria produce called prodigiosin. When enough of them gather on a wet surface, you see a slimy colored ring or patch. This is biology settling out of the air, not a chemical or metal leaching from your pipes.

The most important point is the reassuring one. The pink slime is not a sign that something is wrong with your water. Serratia does not come out of your tap. It floats in on household air and takes hold wherever it finds steady moisture and a bit of food. Public water systems disinfect with chlorine, which keeps treated water free of these bacteria as it travels through the pipes. The pigment only appears after the water leaves the faucet and the bacteria from the air have time to grow on a damp surface.

Gwinnett County's water department, which fields this exact question often, puts it plainly. Its public guidance states that Serratia marcescens "is found naturally in soil, food, and in animals" and that it "tends to grow in bathrooms" on moist surfaces. In other words, this is an indoor housekeeping issue tied to humidity, not a contamination problem you need to test your water for.

Serratia needs three things to bloom: moisture, warmth, and food. A bathroom hands it all three. The bacteria settle out of the air and start feeding on the residue we leave behind every day, mainly soap scum, shampoo and conditioner film, and skin oils. Phosphates that linger on surfaces from some soaps and shampoos give the colony an extra boost.

That is why the slime turns up in predictable spots. You will see it as a ring inside the toilet bowl or under the rim, where standing water never dries out. It collects on the showerhead, in tile grout, on the shower curtain or liner, in soap dishes, and around drains and caulk lines. Pet water bowls and the corners of bathtubs are common too. Each of these places stays wet long enough for the bacteria to multiply and for the pink color to become visible.

One detail surprises people: a brand new bathroom or a recently cleaned one is not immune. Because the bacteria are everywhere in the air, a freshly scrubbed surface simply gives them a clean place to start over. The film is a sign of dampness and leftover residue, not of a dirty home.

You may also notice the slime shows up faster in a bathroom that gets used a lot. Every shower adds steam and a fresh coat of soap and shampoo film, and every hand wash leaves a trace of skin oil and product on the sink and faucet. A guest bathroom that sits unused may stay clear for weeks, while the main shower picks up a pink ring in days. The pattern follows moisture and use, which is another clue that the cause is the room, not the water.

For a healthy person, Serratia marcescens on a bathroom surface is generally harmless. You are not going to get sick from seeing it on your tile, and it is not poisoning your water. That said, it is a bacterium, so you should remove it rather than ignore it. Serratia can cause infection if it reaches the body through a vulnerable route, such as the eyes or an open wound, and it is more of a concern for people with weakened immune systems.

The practical takeaway is calm and simple. Treat the pink film the way you would treat any other bathroom grime. Keep it cleaned up, avoid letting it build up in spots that touch your eyes or cuts, and do not scrub at it bare-handed if you have an open wound. There is no need to stop drinking or using your water, and no need to panic about your home.

It also helps to know what the slime is not. It is not the same as the black slime that can build up inside drains and on aerators, which is usually a biofilm tied to organic matter and sometimes oxidized manganese. And the pink color is unrelated to anything regulated in drinking water. The EPA's secondary drinking water standards cover aesthetic nuisances like staining minerals, but Serratia is an airborne organism that grows on surfaces, so a water test will not explain or fix it. Federal drinking water rules under the EPA test public supplies for dozens of contaminants, none of which is the cause of a pink bathroom ring.

Because the slime is harmless to healthy people, there is no reason to feel uneasy about a colored spot you catch early. The sensible response is to wipe it away and dry the surface, then make the small habit changes below so it has a harder time returning.

Cleaning is straightforward, and you almost certainly have the supplies already. Scrub the affected surfaces with a brush and a bathroom cleaner to break up the colored film and the soap scum feeding it. To disinfect, use a diluted bleach solution. The CDC advises using no more than 1 cup of household bleach per gallon of water for general cleaning and disinfecting, which is plenty strong for bathroom surfaces. Let the solution sit on the surface for several minutes before rinsing so it has time to kill the bacteria.

A few safety notes matter here. Never mix bleach with ammonia or with other cleaners, because the combination can create toxic gas. Open a window or run the bathroom exhaust fan while you work, and wear gloves. For a toilet bowl, pour the diluted bleach in, scrub the ring under the rim, let it sit, then flush.

Removing the slime is only half the job. Because the bacteria are airborne and always present, they will return wherever conditions invite them. To slow that down:

• Run the exhaust fan during and after every shower to pull humidity out of the room.
• Rinse away soap and shampoo residue from tile, the tub, and the showerhead so the bacteria lose their food source.
• Keep surfaces dry. Wipe down the shower walls, squeegee glass, and let curtains spread out to dry instead of bunching up.
• Wash or replace shower curtains and liners regularly, since the film clings to the folds.
• Empty and dry soap dishes and pet bowls rather than letting water stand in them.

If you have cleaned the pink slime and watched it return in a week or two, you have not done anything wrong. Serratia marcescens is airborne and ever-present, so a spotless surface is just a fresh start for the next colony that drifts in and finds moisture. You cannot sterilize the air in a home, and you would not want to. The goal is not to eliminate the bacteria but to deny them the steady dampness and residue they need to grow visibly. Regular cleaning and good ventilation keep them in check.

Phoenix bathrooms can be especially friendly to this bacterium, even in a dry climate. The desert air outside is arid, but the inside of a bathroom is a different world: hot, steamy showers raise the humidity fast, and homes are sealed up and air-conditioned for much of the year. A warm, humid, poorly ventilated bathroom gives Serratia exactly the warm, damp pocket it likes, regardless of how dry it is outdoors. Running the fan and keeping wet surfaces wiped down does more to control the pink film here than anything to do with your water supply.

Phoenix tap water is treated, disinfected with chlorine, and tested against federal standards, so the slime is not a reflection of water quality. If you are curious about what is in your water more broadly, that is a separate question worth its own answer. The pink ring in your shower, though, is a housekeeping matter, and a manageable one. Keep things dry, clean with a diluted bleach solution now and then, and the slime stays away.

For related issues, see our answers on black slime in drains and whether Phoenix tap water is safe to drink.